A client platform such as a processor based system like a personal or handheld computer, or a dedicated device such as an automated teller machine, may need to communicate with an entity, such as a server, in a secure manner. In one example, a personal computer user may desire to use the computer, including software such as a browser executing on an operating system, to securely access a stock account on the web.
Prior to such communication, the client platform usually needs to establish trust with the entity such as the server in the example referenced above. The server may require that the device possess specific security related attributes before the server communicates with the device. In the above example, prior to providing access, the stockbroker's web server may seek reliable information regarding security related characteristics of the user's computer and software executing on the computer.
In some instances this information is provided by a signed attestation report transmitted to the server. Thus the server or other entity, prior to establishing secure communication with the platform, makes an attestation request—and consequently, the server may be termed for the purpose of this scenario, an attestation requestor. The attestation report generated by the client and sent to the server may consist of a description of the platform such as the processor manufacturer and version, chipset manufacturer and version, operating system and version, a list of applications running on the platform and their versions, among other items. The report would then be signed by an attestation identity signature and transmitted to the server, that is, the attestation requestor. The attestation requestor has an attestation identity verification key to verify the attestation identity signature. This verification key may be previously available to the attestation requestor; alternatively, the verification key may be transmitted to the requestor as part of a certificate signed by the manufacturer of the platform. Once verified, the requester can decide by inspecting the received attestation report whether to trust the client platform.
In some instances trust in the attestation report may be increased as a result of the report being generated by a trusted platform module incorporated within the client platform. The trusted platform module may be implemented in hardware, software or firmware and provides a reliable source of trusted platform configuration information trusted by the attestation requester. In such instances, the attestation identity signature is performed by the trusted platform module and the platform configuration information used to create the attestation report is provided by the trusted platform module. Thus by verifying the signature on the attestation report, the requester may verify that the report was generated by a trusted platform module whose characteristics are known.
In one instance, the trusted platform module stores the platform configuration as a set of values in a set of platform configuration registers. Thus one such register may store, for example, the motherboard manufacturer; another, the processor manufacturer; a third, the motherboard version; a fourth, the firmware version for the platform, etc.
More complex data may be stored in the configuration registers. Using a chained hashing technique, a series of items, item1, item2 and item3 may be stored in a single platform configuration register, as follows: Register value is HASH (HASH(HASH(Item 1), HASH(Item 2)), HASH(Item 3)). This allows, for example, the trusted module to record that Item 1 was the first program launched, followed by Item 2 and Item 3.
The mechanism described above for establishing trust generally leads to the attestation requester learning detailed information about the configuration of the client platform from the trusted platform module, including such information as the hardware type and configuration, software available on the platform, software loaded and executing on the platform, network connections to the platform, etc.